1. Field of Endeavor
The present invention relates to a turbomachine blade, in particular to a compressor blade for use in a gas turbine engine. The present invention also relates to a method of manufacturing a turbomachine blade, the method including the step of depositing a corrosion and erosion protective coating on the turbomachine blade body.
2. Brief Description of the Related Art
It is known from the state of the art that turbomachine blades, in particular compressor blades, which are made of metallic material such as stainless steel, are susceptible to corrosion, in particular pitting corrosion.
Pitting corrosion is a form of localized corrosion that leads to the creation of small holes in the metallic material based on galvanic corrosion. As is known, pitting corrosion can be initiated by small surface defects such as scratches, holes or local changes of the composition of the material and it may be aggravated by salt deposits and humidity during operation or stand still of the turbine engine.
Due to water droplets and particulate matter impacting on the leading edge area of compressor blades in a gas turbine, pitting corrosion is a frequently occurring degradation mechanism for compressor blading.
Moreover, pitting corrosion is extremely insidious as it causes only little loss of material with small effects on the metal surface. However, it causes serious damages in the deep structure of the metal. When corrosion pits reach a certain depth, particularly in the leading edge area of the blade, they can lead to the formation of cracks, which may finally result in blade failure due to high cyclic fatigue (HCF).
In order to avoid pitting corrosion, it is known to deposit corrosion protective layers on the blade body material. In recent years, sacrificial slurry coatings have become rather popular for use as corrosion protective layers, in particular for use in the front stages in compressor blading. These coatings are sacrificial because they are attacked instead of the blading material. However, it has become apparent that even sacrificial slurry coatings are prone to degradation in highly erosive conditions, as they typically can be found at the leading edges of compressor blades due to water droplets and particles that hit the blades very hard. Because of local loss of the coating's erosion resistant property, corrosion of the leading edge area may occur.